Yersiniae are known to possess a low-affinity, cell bound Fe 3 plus-transport system and a hemin uptake system which permits use of hemin as a sole source of iron; detectable siderophores are not produced. The characteristics of iron uptake by these systems will be defined with respect to affinitY (K), effects of inhibitors, potential competitors, and roles of lipopolysaccharide and outer membrane proteins as binding sites. The influence of tonB product on iron uptake will be probed with the bacteriocin pesticin. By use of appropriate mutants, the significance of these systems in vivo will be determined in normal and iron-overloaded mice. The role of an extra outer membrane protein unique to avirulent organisms will be investigated with respect to porin activity. The effect of iron-privation in yersiniae will be examined with emphasis on maturation of methylthio groups of UXX-coding tRNAs; ability of such unmatured tRNAS (phenylalanyl and leucyl) to promote post-translational protein modification will be determined. The normal absence of this modification system (Wyb-) in Yersinia pestis will be characterized.